Capacitor-integrated feedthrough assembly with improved grounding for an implantable medical device

ABSTRACT

A feedthrough assembly for use with implantable medical devices having a shield structure, the feedthrough assembly engaging with the remainder of the associated implantable medical device to form a seal with the medical device to inhibit unwanted gas, liquid, or solid exchange into or from the device. One or more feedthrough wires extend through the feedthrough assembly to facilitate transceiving of the electrical signals with one or more implantable patient leads. The feedthrough assembly is connected to a mechanical support which houses one or more filtering capacitors that are configured to filter and remove undesired frequencies from the electrical signals received via the feedthrough wires before the signals reach the electrical circuitry inside the implantable medical device.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/734,146, filed Apr. 11, 2007 now U.S. Pat. No. 7,693,576entitled “CAPACITOR-INTEGRATED FEEDTHROUGH ASSEMBLY FOR AN IMPLANTABLEMEDICAL DEVICE,” which is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates generally to implantable medical devices and moreparticularly to shielded feedthrough structures that connect one or moreimplantable patient leads to various operational circuitry within thehousing of the implantable medical devices while maintaining a hermeticseal of the devices.

BACKGROUND OF THE INVENTION

A variety of implantable medical devices have been developed andemployed for long-term implanted monitoring of one or more patientphysiological conditions and/or delivery of indicated therapy.Implantable cardiac stimulation devices are one particular category ofimplantable devices which are adapted to monitor the patients'physiological conditions, including their cardiac activity, and togenerate and deliver indicated therapy to treat one or more arrhythmicconditions. Implantable cardiac stimulation devices typically includeeither a high voltage circuit for generating high voltage waveforms, alow voltage circuit for generating relatively low voltage pacingstimuli, or both low voltage and high voltage circuits that generatewaveforms for delivery to patient tissue. These devices also typicallyinclude a microprocessor-based controller which regulates the deliveryof the high voltage or pacing pulse waveforms. The high and/or lowvoltage circuits and the controller circuitry are generally encasedwithin a biocompatible can or housing along with a battery to power thedevice.

Implantable cardiac stimulation devices typically also include one ormore implantable patient leads with associated electrodes. Theimplantable patient leads are typically connected at one end to acorresponding electrode that delivers therapy to the patient's heart andat the other end to the high and/or low voltage circuitry and controllerin the can or housing. Because of the highly corrosive liquid implantedenvironment and because the materials and operations of the electricalcircuitry are not compatible unless properly isolated from each other,the connection between the leads and the circuitry inside the housingmust be such that a hermetic seal is maintained. Thus, typically,connections between the electrical circuits disposed inside the housingof the implantable device and the patient leads outside of the housingare achieved through one or more feedthrough assemblies.

The feedthrough assemblies provide for connection between the leadsoutside of the housing and the circuitry inside the housing whilemaintaining a hermetic seal. Additionally, the feedthrough assembly ofan implantable medical device generally includes circuitry for filteringthe electrical signals received through the patient leads so as toattenuate the spectrum of unwanted frequencies before they reach thecircuitry inside the housing of the implantable device. Prior artimplantable cardiac stimulation devices generally achieve this filteringthrough multilayer ceramic type capacitors, such as discoidalcapacitors. These discoidal type capacitors are typically disposedinside the feedthrough assembly. The capacitors are very specialized,difficult to manufacture, and are therefore expensive. Because of thespecialized type capacitors, prior art feedthrough assemblies occupypremium space.

As implantable medical devices are configured to be implanted inside apatient's body, their overall dimension cannot exceed certainpredetermined sizes. An increase in the size of the implantable devicemay result in added discomfort to the patient while a decrease in sizecan reduce potential irritation for the patient. Further, due to thelimited possible size of these devices, the amount of space inside thedevice is also limited. Thus, the size of various components used in animplantable medical device is an important design consideration. Smallercomponents may create space for additional features, while a largercomponent may limit the size for other features and components. Thelarge size of the feedthrough device due to the inclusion of thefiltering capacitors thus reduces the amount of space within the housingthat can be used for circuitry or therapy delivering components. Hence,there is a need for a feedthrough structure that provides filteringcapability but has a reduced footprint within the housing to therebyallow for more space for other components.

SUMMARY

What is described herein is a shielded feedthrough assembly for couplingimplantable patient leads to electrical and other operational circuitryof an implantable medical device. In one implementation, the feedthroughassembly includes one or more feedthrough wires, an insulator, and afeedthrough case. In one embodiment, the feedthrough case is connectedto a mechanical support comprised, in one specific embodiment, ofmultiple ceramic layers. One or more filtering capacitors are disposedinside a wire bonding ceramic substrate of the mechanical support tofilter and inhibit transmission of undesired frequencies from electricalsignals received through the implanted patient leads. The shieldedfeedthrough assembly, feedthrough wires, the mechanical support, and ahousing of the implantable medical device act in combination to providea shield between the environment and the sensitive circuitry of thedevice.

Thus, one embodiment includes an implantable cardiac stimulation devicecomprising at least one lead adapted to be implanted adjacent thepatient's heart so as to delivery therapy to the patient's heart and soas to sense electrical activity indicative of the function of thepatient's heart, a controller that receives signals from the at leastone lead indicative of the electrical activity which is indicative ofthe function of the patient's heart wherein the controller also inducesthe delivery of therapeutic electrical stimulation to the patient'sheart via the at least one lead, a casing that defines a cavity thathouses the controller wherein the casing is adapted to be implantedwithin the body of the patient and inhibit the entry of body fluids intothe cavity of the casing that contains the controller, wherein thecasing defines a feedthrough opening through which the at least onefeedthrough wire extends so as to be communicatively coupled to thecontroller, a feedthrough structure that is positioned within thefeedthrough opening wherein the feedthrough structure comprises the atleast one feedthrough wire which is coupled to the at least one lead, amechanical support having a first surface that is coupled to thefeedthrough structure via the first surface so as to be positionedwithin the casing cavity, wherein the mechanical support defines aninterior volume and wherein the mechanical support defines an openingthrough which the at least one feedthrough wire extends so ascommunicatively couple the controller to the at least one lead, and atleast one filter device positioned within the interior volume of themechanical support wherein the at least one filter device iselectrically coupled to the at least one feedthrough wire so as tofilter unwanted signals received by the at least one feedthrough wire toinhibit transmission of the unwanted signals to the controller andwherein the at least one filter device is coupled to ground via thefirst surface of the mechanical support.

In one embodiment the casing of the implantable cardiac stimulationdevice is formed of a conductive material and the feedthrough structuredefines a structure having a first and a second end that is formed of aconducting material such that when the feedthrough structure ispositioned within the opening in the casing, a Faraday cage isestablished about the controller positioned within the cavity of thecasing.

In one embodiment, the mechanical casing is multi-layer and has at leastone opening that communicates with the first surface. In thisembodiment, the at least one filtering device is electrically coupled tothe first surface via the opening. In another embodiment, multiplelayers of the mechanical casing have conductive traces.

A further embodiment includes an implantable medical device comprisingat least one lead adapted to be implanted within the patient so as toprovide electrical stimulation to the heart of the patient, at least oneelectrical sensor that senses the electrical activity of the heart ofthe patient and transmits electrical signals indicative of theelectrical activity, a controller that induces the at least one lead toprovide electrical stimulation to the heart of the patient wherein thecontroller receives signals from the at least one electrical sensor, abiocompatible device housing encapsulating the controller, a shieldstructure extending within the housing and interposed at leastsubstantially between the at least one sensor and the controller, and amechanical support having a first surface that is electrically coupledto ground wherein the mechanical support is mechanically coupled to theshield structure that includes at least one filtering device positionedwithin an opening that communicates with the first surface so as toremove undesired external frequencies from the electrical signalswherein the at least one filtering device is electrically coupled to thefirst surface via the opening, wherein the mechanical support is encasedin a conductive material and wherein the device housing and at leastportions of the shield structure together define a biocompatible sealencapsulating the controller against material exchange with an implantedenvironment.

Yet another embodiment includes an implantable medical device comprisingone or more leads adapted to be implanted adjacent the patient's heartso as to deliver therapy to the patient's heart and so as to senseelectrical activity indicative of the function of the patient's heart, acontroller configured to receive electrical signals from the one or moreleads indicative of the electrical activity which is indicative of thefunction of the patient's heart, wherein the controller comprises one ormore electrical circuits, a shield structure extending within thehousing and interposed at least substantially between the one or moreleads and the controller, an intermediate wire termination structurethat has a first surface and is coupled to the shield structure andconfigured to receive the one or more leads and connect each of the oneor more leads to one or more of the electrical circuits, wherein theintermediate wire termination structure includes at least one filteringdevice positioned in the interior volume of the wire terminationstructure so as to remove undesired external frequencies from theelectrical signals wherein the at least one filtering device ispositioned within an opening in the intermediate wire terminationstructure that communicates with the first surface and wherein the atleast one filtering device is coupled to ground via the opening and thefirst surface, and a biocompatible device housing encapsulating thecontroller and the intermediate wire termination structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating an implantable stimulationdevice in electrical communication with at least three leads implantedinto a patient's heart for delivering multi-chamber stimulation andshock therapy.

FIG. 2 is a functional block diagram of a multi-chamber implantablestimulation device illustrating the basic elements of a stimulationdevice which can provide cardioversion, defibrillation and pacingstimulation in four chambers of the heart.

FIG. 3 illustrates a schematic frontal view of one embodiment of ashielded feedthrough assembly in an implantable medical device.

FIGS. 4A-4B are top views of one embodiment of a mechanical support inan implantable medical device.

FIG. 4C is a top view of one embodiment of a ceramic layer included inthe mechanical support of FIGS. 4A-4B.

FIG. 5 is a circuit diagram of one embodiment of the filteringcapacitors disposed in the mechanical support of FIGS. 4A-4B.

FIGS. 6A and 6B are top and bottom perspective views illustrating asecond embodiment of a feedthrough assembly.

FIGS. 7A-7C are side cross-sectional, top cross-sectional and detailedside-cross sectional views of the support member of the secondembodiment of the feedthrough assembly of FIGS. 6A and 6B illustratinghow the capacitors of the support member can be grounded via a surface.

FIGS. 8A-8D are side and top cross sectional views of the support memberof FIGS. 6A and 6B taken at two different levels illustrating how thecapacitors and feedthroughs can be interconnected at different levels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made to the drawings wherein like numerals referto like parts throughout. The following description is of the best modepresently contemplated for practicing the invention. This description isnot to be taken in a limiting sense but is made merely for the purposeof describing the general principles of the invention. The scope of theinvention should be ascertained with reference to the issued claims. Inthe description of the invention that follows, like numerals orreference designators will be used to refer to like parts or elementsthroughout.

In one embodiment, as shown in FIG. 1, a device 10 comprising animplantable cardiac stimulation device 10, is in electricalcommunication with a patient's heart 12 by way of three leads, 20, 24and 30, suitable for delivering multi-chamber stimulation and shocktherapy. To sense atrial cardiac signals and to provide right atrialchamber stimulation therapy, the stimulation device 10 is coupled to animplantable right atrial lead 20 having at least an atrial tip electrode22, which typically is implanted in the patient's right atrialappendage.

To sense left atrial and ventricular cardiac signals and to provide leftchamber pacing therapy, the stimulation device 10 is coupled to a“coronary sinus” lead 24 designed for placement in the “coronary sinusregion” via the coronary sinus ostium (OS) for positioning a distalelectrode adjacent to the left ventricle and/or additional electrode(s)adjacent to the left atrium. As used herein, the phrase “coronary sinusregion” refers to the vasculature of the left ventricle, including anyportion of the coronary sinus, great cardiac vein, left marginal vein,left posterior ventricular vein, middle cardiac vein, and/or smallcardiac vein or any other cardiac vein accessible by the coronary sinus.

Accordingly, an exemplary coronary sinus lead 24 is designed to receiveatrial and ventricular cardiac signals and to deliver left ventricularpacing therapy using at least a left ventricular tip electrode 26, leftatrial pacing therapy using at least a left atrial ring electrode 27,and shocking therapy using at least a left atrial coil electrode 28.

The stimulation device 10 is also shown in electrical communication withthe patient's heart 12 by way of an implantable right ventricular lead30 having, in this embodiment, a right ventricular tip electrode 32, aright ventricular ring electrode 34, a right ventricular (RV) coilelectrode 36, and a superior vena cava (SVC) coil electrode 38.Typically, the right ventricular lead 30 is transvenously inserted intothe heart 12 so as to place the right ventricular tip electrode 32 inthe right ventricular apex so that the RV coil electrode 36 will bepositioned in the right ventricle and the SVC coil electrode 38 will bepositioned in the superior vena cava. Accordingly, the right ventricularlead 30 is capable of receiving cardiac signals, and deliveringstimulation in the form of pacing and shock therapy to the rightventricle.

As illustrated in FIG. 2, a simplified block diagram is shown of themulti-chamber implantable stimulation device 10, which is capable oftreating both fast and slow arrhythmias with stimulation therapy,including cardioversion, defibrillation, and pacing stimulation. While aparticular multi-chamber device is shown, this is for illustrationpurposes only and one of skill in the art could readily duplicate,eliminate or disable the appropriate circuitry in any desiredcombination to provide a device capable of treating the appropriatechamber(s) with cardioversion, defibrillation and pacing stimulation.

A housing 40 for the stimulation device 10, shown schematically in FIG.2, is often referred to as the “can”, “case” or “case electrode” and maybe programmably selected to act as the return electrode for all“unipolar” modes. The housing 40 may further be used as a returnelectrode alone or in combination with one or more of the coilelectrodes, 28, 36 and 38, for shocking purposes. The housing 40 furtherincludes a connector (not shown) having a plurality of terminals, 42,44, 46, 48, 52, 54, 56, and 58 (shown schematically and, forconvenience, the names of the electrodes to which they are connected areshown next to the terminals). As such, to achieve right atrial sensingand pacing, the connector includes at least a right atrial tip terminal(A_(R) TIP) 42 adapted for connection to the atrial tip electrode 22.

To achieve left chamber sensing, pacing and shocking, the connectorincludes at least a left ventricular tip terminal (V_(L) TIP) 44, a leftatrial ring terminal (A_(L) RING) 46, and a left atrial shockingterminal (A_(L) COIL) 48, which are adapted for connection to the leftventricular tip electrode 26, the left atrial ring electrode 27, and theleft atrial coil electrode 28, respectively.

To support right chamber sensing, pacing and shocking, the connectorfurther includes a right ventricular tip terminal (V_(R) TIP) 52, aright ventricular ring terminal (V_(R) RING) 54, a right ventricularshocking terminal (R_(V) COIL) 56, and an SVC shocking terminal (SVCCOIL) 58, which are adapted for connection to the right ventricular tipelectrode 32, right ventricular ring electrode 34, the RV coil electrode36, and the SVC coil electrode 38, respectively.

At the core of the stimulation device 10 is a programmablemicrocontroller 60 which controls the various modes of stimulationtherapy. As is well known in the art, the microcontroller 60 typicallyincludes a microprocessor, or equivalent control circuitry, designedspecifically for controlling the delivery of stimulation therapy and mayfurther include RAM or ROM memory, logic and timing circuitry, statemachine circuitry, and I/O circuitry. Typically, the microcontroller 60includes the ability to process or monitor input signals (data) ascontrolled by a program code stored in a designated block of memory. Thedetails of the design and operation of the microcontroller 60 are notcritical to the invention. Rather, any suitable microcontroller 60 maybe used that carries out the functions described herein. The use ofmicroprocessor-based control circuits for performing timing and dataanalysis functions are well known in the art.

As shown in FIG. 2, an atrial pulse generator 70 and a ventricular pulsegenerator 72 generate pacing stimulation pulses for delivery by theright atrial lead 20, the right ventricular lead 30, and/or the coronarysinus lead 24 via an electrode configuration switch 74. It is understoodthat in order to provide stimulation therapy in each of the fourchambers of the heart, the atrial and ventricular pulse generators, 70and 72, may include dedicated, independent pulse generators, multiplexedpulse generators, or shared pulse generators. The pulse generators, 70and 72, are controlled by the microcontroller 60 via appropriate controlsignals, 76 and 78, respectively, to trigger or inhibit the stimulationpulses.

The microcontroller 60 further includes timing control circuitry 79which is used to control the timing of such stimulation pulses (e.g.,pacing rate, atrio-ventricular (AV) delay, atrial interconduction (A-A)delay, or ventricular interconduction (V-V) delay, etc.) as well as tokeep track of the timing of refractory periods, noise detection windows,evoked response windows, alert intervals, marker channel timing, etc.,which is well known in the art.

The switch 74 includes a plurality of switches for connecting thedesired electrodes to the appropriate I/O circuits, thereby providingcomplete electrode programmability. Accordingly, the switch 74, inresponse to a control signal 80 from the microcontroller 60, determinesthe polarity of the stimulation pulses (e.g., unipolar, bipolar,combipolar, etc.) by selectively closing the appropriate combination ofswitches (not shown) as is known in the art. In this embodiment, theswitch 74 also supports simultaneous high resolution impedancemeasurements, such as between the case or housing 40, the right atrialelectrode 22, and right ventricular electrodes 32, 34 as described ingreater detail below.

Atrial sensing circuits 82 and ventricular sensing circuits 84 may alsobe selectively coupled to the right atrial lead 20, coronary sinus lead24, and the right ventricular lead 30, through the switch 74 fordetecting the presence of cardiac activity in each of the four chambersof the heart. Accordingly, the atrial (ATR. SENSE) and ventricular (VTR.SENSE) sensing circuits, 82 and 84, may include dedicated senseamplifiers, multiplexed amplifiers, or shared amplifiers. The switch 74determines the “sensing polarity” of the cardiac signal by selectivelyclosing the appropriate switches, as is also known in the art. In thisway, the clinician may program the sensing polarity independently of thestimulation polarity.

Each sensing circuit, 82 and 84, preferably employs one or more lowpower, precision amplifiers with programmable gain and/or automatic gaincontrol, bandpass filtering, and a threshold detection circuit, as knownin the art, to selectively sense the cardiac signal of interest. Theautomatic gain control enables the device 10 to deal effectively withthe difficult problem of sensing the low amplitude signalcharacteristics of atrial or ventricular fibrillation. The outputs ofthe atrial and ventricular sensing circuits, 82 and 84, are connected tothe microcontroller 60 which, in turn, are able to trigger or inhibitthe atrial and ventricular pulse generators, 70 and 72, respectively, ina demand fashion in response to the absence or presence of cardiacactivity in the appropriate chambers of the heart.

For arrhythmia detection, the device 10 utilizes the atrial andventricular sensing circuits, 82 and 84, to sense cardiac signals todetermine whether a rhythm is physiologic or pathologic. As used herein“sensing” is reserved for the noting of an electrical signal, and“detection” is the processing of these sensed signals and noting thepresence of an arrhythmia. The timing intervals between sensed events(e.g., P-waves, R-waves, and depolarization signals associated withfibrillation) are then classified by the microcontroller 60 by comparingthem to a predefined rate zone limit (i.e., bradycardia, normal, lowrate VT, high rate VT, and fibrillation rate zones) and various othercharacteristics (e.g., sudden onset, stability, physiologic sensors, andmorphology, etc.) in order to determine the type of remedial therapythat is needed (e.g., bradycardia pacing, anti-tachycardia pacing,cardioversion shocks or defibrillation shocks, collectively referred toas “tiered therapy”).

Cardiac signals are also applied to the inputs of an analog-to-digital(A/D) data acquisition system 90. The data acquisition system 90 isconfigured to acquire intracardiac electrogram (IEGM) signals, convertthe raw analog data into a digital signal, and store the digital signalsfor later processing and/or telemetric transmission to an externaldevice 102. The data acquisition system 90 is coupled to the rightatrial lead 20, the coronary sinus lead 24, and the right ventricularlead 30 through the switch 74 to sample cardiac signals across any pairof desired electrodes.

The microcontroller 60 is further coupled to a memory 94 by a suitabledata/address bus 96, wherein the programmable operating parameters usedby the microcontroller 60 are stored and modified, as required, in orderto customize the operation of the stimulation device 10 to suit theneeds of a particular patient. Such operating parameters define, forexample, pacing pulse amplitude, pulse duration, electrode polarity,rate, sensitivity, automatic features, arrhythmia detection criteria,and the amplitude, waveshape and vector of each shocking pulse to bedelivered to the patient's heart 12 within each respective tier oftherapy.

Advantageously, the operating parameters of the implantable device 10may be non-invasively programmed into the memory 94 through a telemetrycircuit 100 in telemetric communication with the external device 102,such as a programmer, transtelephonic transceiver, or a diagnosticsystem analyzer. The telemetry circuit 100 is activated by themicrocontroller by a control signal 106. The telemetry circuit 100advantageously allows IEGMs and status information relating to theoperation of the device 10 (as contained in the microcontroller 60 ormemory 94) to be sent to the external device 102 through an establishedcommunication link 104.

In the preferred embodiment, the stimulation device 10 further includesa physiologic sensor 108, commonly referred to as a “rate-responsive”sensor because it is typically used to adjust pacing stimulation rateaccording to the exercise state of the patient. However, thephysiological sensor 108 may further be used to detect changes incardiac output, changes in the physiological condition of the heart, ordiurnal changes in activity (e.g., detecting sleep and wake states).Accordingly, the microcontroller 60 responds by adjusting the variouspacing parameters (such as rate, AV Delay, V-V Delay, etc.) at which theatrial and ventricular pulse generators, 70 and 72, generate stimulationpulses.

The stimulation device additionally includes a battery 110 whichprovides operating power to all of the circuits shown in FIG. 2. For thestimulation device 10, which employs shocking therapy, the battery 110is generally capable of operating at low current drains for long periodsof time and then be capable of providing high-current pulses (forcapacitor charging) when the patient requires a shock pulse. The battery110 generally also has a predictable discharge characteristic so thatelective replacement time can be detected. Accordingly, embodiments ofthe device 10 including shocking capability preferably employlithium/silver vanadium oxide batteries. For embodiments of the device10 not including shocking capability, the battery 110 will preferably belithium iodide or carbon monoflouride or a hybrid of the two.

As further shown in FIG. 2, the device 10 is shown as having animpedance measuring circuit 112 which is enabled by the microcontroller60 via a control signal 114.

In the case where the stimulation device 10 is intended to operate as animplantable cardioverter/defibrillator (ICD) device, it generally shoulddetect the occurrence of an arrhythmia, and automatically apply anappropriate electrical shock therapy to the heart aimed at terminatingthe detected arrhythmia. To this end, the microcontroller 60 furthercontrols a shocking circuit 116 by way of a control signal 118. Theshocking circuit 116 generates shocking pulses of low (up to 0.5joules), moderate (0.5-10 joules), or high energy (11 to 40 joules), ascontrolled by the microcontroller 60. Such shocking pulses are appliedto the patient's heart 12 through at least two shocking electrodes, andas shown in this embodiment, selected from the left atrial coilelectrode 28, the RV coil electrode 36, and/or the SVC coil electrode38. As noted above, the housing 40 may act as an active electrode incombination with the RV electrode 36, or as part of a split electricalvector using the SVC coil electrode 38 or the left atrial coil electrode28 (i.e., using the RV electrode as a common electrode).

Cardioversion shocks are generally considered to be of low to moderateenergy level (so as to minimize pain felt by the patient), and/orsynchronized with an R-wave and/or pertaining to the treatment oftachycardia. Defibrillation shocks are generally of moderate to highenergy level (i.e., corresponding to thresholds in the range of 5-40joules), delivered asynchronously (since R-waves may be toodisorganized), and pertaining exclusively to the treatment offibrillation. Accordingly, the microcontroller 60 is capable ofcontrolling the synchronous or asynchronous delivery of the shockingpulses.

FIG. 3 illustrates a partial frontal view of one embodiment of ashielded feedthrough assembly 300 engaged to the housing of animplantable medical device, such as the device 10 of FIG. 1. Thefeedthrough assembly 300 is used in this embodiment to, among otherthings, connect one or more implantable patient leads to electrical orother operational circuitry inside the housing 40 of the implantablemedical device 10.

The feedthrough assembly 300, in this particular implementation,includes three feedthrough wires 310, an insulator 320, and afeedthrough case 330. As illustrated, the feedthrough assembly 300extends through a hermetically sealed outer wall of the housing 40 andinto the housing 40 to couple one or more implantable patient leads toan electronic hybrid and controller board 360 while maintaining ahermetical seal.

The feedthrough wires 310 receive electrical signals from the patientleads and transfer the signals through the feedthrough assembly 300 tothe circuitry inside the housing 40. Thus, the feedthrough wires 310 arelead wires that are each configured for connection, at an upper end, toa patient lead such as the leads 20, 24, or 30 of FIG. 1. Thefeedthrough wires 310 are, in one embodiment, connected to the patientleads through one or more connectors. In one configuration, theconnectors are located in one or more headers such as the headers 11shown in FIG. 1. In another embodiment, the connection between thefeedthrough wires 310 and the patient leads can be achieved throughwelding or brazing. In yet another embodiment, the feedthrough wires 310may form the patient leads by extending out of the feedthrough assemblyand into the patient's body.

Each of the feedthrough wires 310 extend through respective openings inthe insulator 320 towards the feedthrough case 330 and a mechanicalsupport 340. Because the feedthrough wires 310 are configured to beplaced in an implanted location, the feedthrough wires 310 arepreferably comprised of electrically conductive biocompatible materials.In one embodiment, the feedthrough wires 310 are comprised of aplatinum-iridium alloy. In other embodiments, other suitable conductivebiocompatible materials such as platinum, nobium, titanium, tantalum, orcombinations of these alloys can be used. In yet other embodiments, thefeedthrough wires 310 may be provided with a biocompatible coating orfinish.

Although, the feedthrough assembly 300 of FIG. 3 includes threefeedthrough wires, it should be understood that depending on the numberof implantable patient leads in a given implantable device, otherembodiments may include more or less than three feedthrough wires. Forexample, in an embodiment where only one patient lead is implantedwithin the body of the patient, the feedthrough assembly includes onlyone feedthrough wire. Other implementations are also possible. Forexample, in some embodiments one feedthrough wire may be used totransfer signals from more than one patient lead. In other embodiments,the number of the feedthrough wires may exceed the number of implantablepatient leads.

The feedthrough wires extend through the insulator 320. The insulator320 is interposed between the outside environment where the device isimplanted and the inside of the housing 40 of the implantable device 10.The insulator 320 has an outer surface 325 and an inner surface 327. Asthe outer surface 325 of the insulator 320 is, in this embodiment,exposed to the implanted environment, it is generally formed ofbiocompatible materials or is provided with a biocompatible coating orfinish. The inner surface 327 of the insulator 320 connects theinsulator 320 to the feedthrough case 330.

The feedthrough case 330 fits inside an opening (not shown) in thehermetically sealed outer wall of the housing 40 such that there iscomplete insulation between the outside environment and the inside ofthe housing 40. In one embodiment, this insulation is achieved by usinga hermetic seal 335. When the feedthrough case 330 is placed inside theopening, the hermetic seal 335 is wrapped around an upper portion of thefeedthrough case 330 and completely seals the inside of the housing 40from the outside environment. A variety of other methods are alsopossible.

In one embodiment, the feedthrough case 330 includes three openingsthrough which the feedthrough wires 310 extend. The feedthrough case 330is also connected to the mechanical support 340. In one embodiment, themechanical support 340 acts as an interface between the feedthroughwires 310 and the hybrid and controller board 360.

Generally, implantable medical devices such as, for example, the device10 of FIG. 1, need to include a large number of connections between thevarious electronic circuits inside the housing 40 and one or morefeedthrough wires, such as feedthrough wires 310. Because of the limitedspace available inside an implantable medical device, routing of themany different wires and directly connecting the different circuits tothe wires has become increasingly difficult. The mechanical support 340provides an interface through which the one or more feedthrough wires310 can be efficiently connected to the various electronic circuitswithout requiring too much space. As will be discussed below, themechanical support 340 includes an interior volume in which a pluralityof traces can be formed so as to facilitate routing of electricalconductors in an efficient manner. Hence, the mechanical support 340provides an intermediate routing component that allows for electricalconductors carrying signals to be re-routed so that the conductorsoccupy less volume and are better isolated from each other.

In addition to being an interface for wire connections, the mechanicalsupport 340 can be used to house one or more circuits used for filteringthe electronic signals. Generally, implantable patient leads of animplantable device are formed of materials that provide goodconductivity. However, because of their high conductivity properties,these leads sometimes act as an antenna and conduct undesiredelectromagnetic interference signals (EMI). These undesired signals, iftransmitted to the circuitry of the housing 40, can interfere with andadversely affect the normal operations of the device 10. Thus,implantable medical devices generally include filtering circuits thatattenuate undesired signals before they reach the electronic circuitryof the housing 40. Previously, these filtering circuits were made of oneor more discoidal type capacitors that were disposed inside thefeedthrough case 330. These discoidal type capacitors are generallyspecialized, need to be custom built, and are thus expensive tomanufacture.

In order to reduce the overall size of the feedthrough assembly, makemore efficient use of the limited space of the housing, and provide amore cost-effective feedthrough assembly, in one or more embodiments ofthe present invention, instead of being placed inside the feedthroughcase 330, the filtering capacitors are integrated into the mechanicalsupport 340. Additionally, manufacturing costs are further reduced byusing commonly-produced capacitors that are more cost-effective thandiscoidal type capacitors.

FIGS. 4A-4C illustrate in more detail one embodiment of the mechanicalsupport 340. The mechanical support 340 is a multilayer structure whichincludes multiple electrically insulated layers, preferably made ofceramic in one implementation, and includes one or more openings 410through which one or more feedthrough wires, such as the feedthroughwires 310 of FIG. 3, can extend.

Additionally, the mechanical support 340 includes multiple wire-bondpads 430 that are attached to a bottom layer 460. In this embodiment,the bottom layer 460 is used with three feedthrough wires 310. In someother embodiments, the bottom layer 460 is used with four feedthroughwires in a quad polar feedthrough. In yet other embodiments, the bottomlayer 460 is used with six feedthrough wires in a hex polar feedthrough.Generally, whether or not they are used, all pads 430 are wire bonded toeliminate mistakes. The wire-bond pads 430 are connected at least on oneside to a bottom surface of the feedthrough case 330 of FIG. 3. In oneembodiment, the wire-bond pads 430 are wire-bonded to the internalelectronics of the hybrid and controller board 360. As illustrated inFIG. 3, each of the wire-bond pads 430 is connected through at least oneconnector 355 to the hybrid and controller board 360. Thus, thewire-bond pads 430 facilitate the transfer of signals from thefeedthrough wires 310 to the electronic circuits of the housing 40.

As illustrated in FIG. 4A, one or more top layers of the mechanicalsupport 340 also include four openings 420 configured for receiving fourcapacitors. As illustrated, the openings 410 extend through one or more,but not all, layers of the mechanical support 340. At lease one layer ofthe mechanical support 340, such as the layer 440 illustrated in FIG.4C, includes one or more traces 445 that connect the openings 410 to thewire-bond pads 430. Thus, when capacitors 450, illustrated in FIG. 4B,are placed inside the openings 420, the traces 445 each connect one sideof the capacitors 450 to one of the openings 410 and the other side ofthe capacitors 450 to one of the wire-bond pads 430. At least one of thewire bond pads 430 is connected to the outer surface of the feedthroughcase 330 and thus acts as the system ground for the mechanical support340. Thus in effect, the traces 445 connect the capacitors 450 betweenthe feedthrough wires 310 and the system ground.

In one embodiment, the mechanical support 340 also includes a metalshield 350 (shown in FIG. 3) which forms the outside surface of themechanical support 340. By encasing the mechanical support 340, themetal shield 350 creates a Faraday cage effect inside the mechanicalsupport 340. The Faraday cage effect blocks external electrical fieldsand thus in effect inhibits external undesired frequencies from enteringthe mechanical support 340 thus shielding the conductors positionedtherein. In other embodiments, the Faraday cage effect is achieved bymetallization of the outer surface of the mechanical support 340.

The mechanical support 340 of FIGS. 4A-4C is a quad-polar structure.Alternative configurations of the mechanical support 340 are alsopossible. For example, in one embodiment, the mechanical support 340 canform a hex-polar structure. Other embodiments are also possible. Forexample, in one embodiment, each of the traces 445 of the mechanicalsupport 340 is placed on a separate layer of the mechanical support 340.In another embodiment, different layers include two or more, but not allthe traces 445.

A mechanical support of a feedthrough assembly is generally manufacturedby stacking the various layers that form the mechanical structure on topof one another and laminating the stack with printing to form anassembly. The assembly is then fired into a final state. Inimplementations where the various layers are formed of ceramic, thefiring generally needs to be done at a high temperature to assure properprocessing.

A mechanical support 340 of an embodiment of the present invention, ismanufactured, in one implementation, by stacking the one or more layerson top of one another, placing the one or more capacitors 450 into theopenings 420, and encasing the mechanical support 340 into the metalshield 350 to form an assembly before firing the assembly into a finalstate. However, in configurations where the various layers are formed ofceramic, the various layers may be stacked on top of another and firedinto a final state before connecting the capacitors to the resultingassembly. This may be done in some embodiments, because the hightemperature required for firing ceramic layers may in some instancescause damage to some capacitors. Therefore, in one embodiment, thecapacitors are connected to the mechanical support 340 through solderingor other similar methods known in the art, after the layers have beenfired.

FIG. 5 illustrates one exemplary embodiment of a circuit diagram showingthe connections between the capacitors 450 of FIG. 4B and one or morefeedthrough wires 310. Each of the capacitors 510-540 of FIG. 5illustrates one of the capacitors 450 of FIG. 4B. As illustrated, acapacitor 510 is connected between a pin 1 and the ground. Pin 1 isconnected to one of the feedthrough wires 310 which is itself connectedto the implantable right atrial lead 20 of FIG. 1. Because the lead 20is itself coupled to the right atrial tip electrode 22 of FIG. 1, thecapacitor 510 is thus connected to and receives signals from the rightatrial tip electrode (AT) 22.

Similarly, pins 2 and 3 of FIG. 5 are connected to feedthrough wires 310that are themselves connected to the coronary sinus lead 24 of FIG. 1.The coronary sinus lead 24 is coupled to the left atrial ring electrode(AR) 27 and the left ventricular tip electrode (VT) 26. Thus thecapacitor 520 which is connected to pin 2 is connected to and receivessignals from the left atrial ring electrode (AR) 27 and the capacitor530 which is connected to pin 3 is connected to and receives signalsfrom the left ventricular tip electrode (VT) 26.

In a similar manner, the capacitor 540 which is connected to pin 4 isconnected to a feedthrough wire 310 coupled to the right ventricularlead 30 of FIG. 1. Thus, because the right ventricular lead 30 iscoupled to the right ventricular ring (VR) 34 of FIG. 1, the capacitor540 is connected to and receives signals from the right ventricular ring(VR) 34.

The capacitors 510-540 are chosen such that they can filter and removeundesired frequencies from the electrical signals they receive. Becauseall four capacitors are connected to the system ground, the undesiredfrequencies are passed directly to the system ground before they canreach the electrical circuitry of the housing 40 and result in anyadverse effects.

It will be appreciated that in various embodiments the materials andprocesses selected can be adapted to the structural and electricalrequirements as well as to the expected operating environment of theparticular application. For example, as the insulator 320 and thefeedthrough wires 310 are in certain embodiments not exposed to theexternal implanted environment, the insulator 320 and the feedthroughwires 310 can comprise materials and processes which are not generallyconsidered biocompatible, such as solder and/or certain conductivematerials.

FIGS. 6A and 6B illustrate an alternative embodiment of a feedthroughassembly 600 similar to the assembly 300 described above. In thisimplementation, a mechanical support 640 has been modified to providefor a more efficient use of the interior space of the mechanical support640. As shown in FIGS. 6A and 6B, the assembly 600 includes feedthroughwires 610 that can be coupled to the leads 22, 24, 30 in the same manneras described above. The feedthrough wires enter into a feedthrough case630 that is substantially similar to the case 330 described above andincludes an insulator 620 and a hermetic seal 635 that engages with thehousing 40 in the same manner as described above.

The case 630 is mounted on an upper surface 641 of a mechanical support640 of the present embodiment. The upper surface 641 of the mechanicalsupport 640 include openings 651 that receive capacitors 750 in asimilar manner as described above. The mechanical support 640 furtherincludes openings 710 that receive the feedthroughs 610 in the samemanner as the openings 410 described above in conjunction with FIGS.4A-C. In this implementation, the configuration of the interior space ofthe mechanical support 640 has been re-oriented so as to increase theamount of space that can be used for positioning the capacitors 750 sothat the capacitors 750 are positioned more closely to the feedthroughs610 to thereby reduced parasitic inductances.

The mechanical support further includes wire bonding pads 730 that allowfor wire bond connections via connectors 355 to a hybrid and boardcontroller 360 in substantially the same manner as described inconjunction with FIG. 3 above. As shown in FIGS. 6A and 6B, however, aconductive ground connection 740 extends from the upper surface 641 ofthe mechanical support to a lower surface 642. In this implementation,both the upper surface 641 and the lower surface 642 of the mechanicalsupport 640 are coated with a conductive coating. In one implementation,the upper surface 641 and the lower surface 642 are plated with anelectrolytic nickel and gold using a well-known process. The conductiveground connection 740 thereby provides a uniform ground connectionbetween the surfaces 641 and 642. Further the side surfaces, other thanthe surface having the wire bonding pads 730 may also be coated forshielding purposes in the manner described above.

In the embodiment discussed above in connection with FIGS. 3 and 4, thecapacitors 420 are connected to ground via traces 445 formed in a layerwithin the mechanical support 340. In some circumstances, this canresult in the loss of volume for the connection of the capacitors to thefeedthrough which can result in the feedthrough being separated from thecapacitors 750. This greater spacing can result in an increase in theparasitic capacitances and inductances which can affect the transmissionof signals into the interior of the housing 40 which can potentiallyaffect the overall operation of the device.

To address this issue, the embodiment of FIGS. 6-8 connects thecapacitors 750 to ground via the conductive upper surface 641 of themechanical support 640. More specifically, referring to FIGS. 7A-7C, thecapacitors 750 are positioned within the openings 651. One end of thecapacitors 750 are connected to the feedthroughs 610 via traces 645 inthe same manner as discussed above so as to achieve a grounding circuitsimilar to that shown in FIG. 5. As shown in FIG. 7C, the traces 645 arelocated proximate the bottom surface 642 of the mechanical support 640on one or more levels as will be discussed in greater detailhereinbelow.

The openings 651 are exposed to the upper surface 641 of the mechanicalsupport 640 and a conductive material 647, such as conductive polymer,is used to fill the openings up to the level of the surface 641 tothereby electrically interconnect the capacitors 750 to the surface 641.In this way, all of the capacitors 750 can be coupled to the uppersurface 641 of the mechanical support 340 and then subsequently becoupled to ground, in a manner that will be described hereinbelow,without requiring a layer of traces to be formed within the interior ofthe mechanical support 640. The electrical connection between thecapacitors 750 and the surface 641 can be accomplished in any of anumber of ways including the use of conductive epoxy, solder and thelike.

Referring back to FIG. 6A, the feedthrough case 630 is preferably madeof a conductive material such as titanium and can be electricallycoupled to the upper surface 641 of the mechanical support 640 as aresult of physical contact. As is also illustrated in FIG. 6A, aconductive polymer bead 680 or like structure may also be positionedabout the outer circumference of the feedthrough case 630 wherein thefeedthrough case 630 is positioned proximate the upper surface 641 tothereby enhance the electrical interconnection. As discussed above inconnection with the embodiment of FIGS. 3 and 4, the feedthrough case630 is electrically coupled to the housing 40 which serves as ground.

Thus, by coating the upper surface 641 with a conductive material andelectrically connecting the capacitors 750 to the upper surface 641 viasolder or conductive polymer, the capacitors 750 can be coupled toground via the feedthrough case 630 without requiring the use of a layerof wiring traces within the mechanical support 640. This increases theamount of available space to form the traces to connect the capacitors750 to the feedthroughs 610 thereby improving the function of the deviceas described above.

As is also illustrated in FIGS. 7A-7C and 8A-8D, the interconnection ofthe feedthrough 610 to the wire bond pads 730 may be formed on aplurality of different levels within the mechanical support 640. Morespecifically, in the exemplary embodiment shown in FIGS. 8A and 8B,three of the feedthroughs 610 a-610 c may be connected to capacitors 750a-750 c and corresponding wire bond pads 730 a-730 c via traces 645a-645 c on one vertical level B-B of the mechanical support 640.Further, a higher level C-C shown in FIGS. 8C and 8D may be used toconnect a fourth feedthrough 610 d to a capacitor 750 d and a wire bondpad 730 d via a trace 645 d. By offsetting the traces 645 in a verticaldirection, the feedthroughs 610 can be positioned more closely to thewire bonds 730 which can further reduce parasitic capacitances andinductances and thereby improve the performance of the device.

Thus, various embodiments of the present invention provide thecapability to incorporate signal filtering into implantable medicaldevice applications. Various embodiments provide and maintain aneffective hermetic seal such that possible harmful contaminants areinhibited from entry to or exit from an implantable medical device whichmight otherwise interfere with intended operation of the device, and/orcause injury to the patient. Various embodiments also shield or inhibitinterference between various electronic modules of an implantablemedical device. The various embodiments facilitate reducing the size andthe cost of a feedthrough assembly used in implantable medical devices.

Although the above disclosed embodiments of the present teachings haveshown, described and pointed out the fundamental novel features of theinvention as applied to the above-disclosed embodiments, it should beunderstood that various omissions, substitutions, and changes in theform of the detail of the devices, systems and/or methods illustratedmay be made by those skilled in the art without departing from the scopeof the present teachings. Consequently, the scope of the inventionshould not be limited to the foregoing description but should be definedby the appended claims.

1. An implantable cardiac stimulation device comprising: at least onelead adapted to be implanted adjacent the patient's heart so as todelivery therapy to the patient's heart and so as to sense electricalactivity indicative of the function of the patient's heart; a controllerthat receives signals from the at least one lead indicative of theelectrical activity which is indicative of the function of the patient'sheart wherein the controller also induces the delivery of therapeuticelectrical stimulation to the patient's heart via the at least one lead;a casing that defines a cavity that houses the controller wherein thecasing is adapted to be implanted within the body of the patient andinhibit the entry of body fluids into the cavity of the casing thatcontains the controller, wherein the casing defines a feedthroughopening through which the at least one feedthrough wire extends so as tobe communicatively coupled to the controller and wherein the casingdefines a ground for the implantable cardiac stimulation device; afeedthrough structure that is positioned within the feedthrough openingwherein the feedthrough structure comprises the at least one feedthroughwire which is coupled to the at least one lead; a mechanical supporthaving a first surface that is coupled to the feedthrough structure viathe first surface so as to be positioned within the casing cavity,wherein the mechanical support defines an interior volume and whereinthe mechanical support defines an opening through which the at least onefeedthrough wire extends so as communicatively couple the controller tothe at least one lead; and at least one filter device positioned withinthe interior volume of the mechanical support wherein the at least onefiltering device is electrically coupled to the at least one feedthroughwire so as to filter unwanted signals received by the at least onefeedthrough wire to inhibit transmission of the unwanted signals to thecontroller and wherein the at least one filter device is coupled toground via the first surface of the mechanical support.
 2. The device ofclaim 1, wherein the casing is formed of a conductive material and thefeedthrough structure defines a structure having a first and a secondend that is formed of a conducting material such that when thefeedthrough structure is positioned within the opening in the casing, aFaraday cage is established about the controller positioned within thecavity of the casing.
 3. The device of claim 1, wherein the mechanicalsupport is formed of a multi-layer ceramic material having openings andtraces within the interior volume so as to allow electricalinterconnection between the at least one filtering device and the atleast one feedthrough wire.
 4. The device of claim 3, wherein themulti-layer ceramic material comprises at least one opening though whichthe at least one filtering device extends wherein the openingcommunicates with the first surface.
 5. The device of claim 4, whereinthe first surface is conductive and a conductive material is positionedwithin the opening so as to extend from the at least one filteringdevice and the conductive first surface.
 6. The device of claim 5,wherein the feedthrough structure is also conductive and is positionedon the first surface so as to be conductively linked to the at least onefiltering device.
 7. The device of claim 6, wherein the feedthroughstructure is conductively coupled with the case.
 8. The device of claim6, wherein the feedthrough structure is further coupled to the firstsurface via a conductive solder.
 9. The device of claim 3, wherein themechanical support is comprised of a top, a middle, and a bottom ceramiclayer.
 10. The device of claim 9, wherein the top and the middle ceramiclayers comprise at least one opening though which the at least onefiltering device extends.
 11. The device of claim 9, wherein traces aredisposed on the bottom ceramic layer.
 12. The device of claim 11,wherein traces are disposed on a plurality of ceramic layers.
 13. Thedevice of claim 3, wherein the at least one filter device comprises atleast one capacitor that is adapted for filtering undesired EMIfrequencies.
 14. The device of claim 13, wherein the mechanical supportcomprises four capacitors which are electrically coupled to at least onewire bond pad.
 15. The device of claim 1, wherein the mechanical supportis encased in a conductive material, such that a Faraday cage isestablished about the mechanical support.
 16. The device of claim 1,wherein the at least one lead comprises a pacing lead adapted to providelow voltage pacing pulses to the heart.
 17. The device of claim 1,wherein the at least one lead comprises a high voltage lead adapted toprovide high voltage cardioversion or defibrillation waveforms to thepatient's heart.